The present invention relates generally to a shift control system for vehicular drive lines and more particularly to a semi-automatic shift control system suitable for heavy duty trucks that utilizes torque modulation to improve gear disengagement and shift control. The present invention also includes a method for improving gear disengagement and shift control.
Vehicle transmissions are well known in the art. Heavy duty vehicles typically include a manual or a semi-automatic transmission. The basic principal behind such semi-automatic transmissions is to assist a driver in performing a manually selected gear ratio change using a system that is at least partially automated. While such transmissions are becoming more prevalent, those skilled in the art continue to attempt to improve or enhance current designs.
To effect a gear change or shift in vehicles with a conventional manual transmission, the driver manually operates a clutch and a gear shift lever. The master clutch disengages the output shaft of the engine from the input shaft of the transmission so that the transmission is moved out of engagement with a pre-selected gear and into a neutral position. The master clutch is then released to allow the internal rotating members of the transmission to maintain their rotational speed and approximates a desired engine speed via the engine throttle that corresponds to an appropriate synchronized speed for engaging the new gear. Then, to re-engage the transmission into a new pre-selected gear, the driver operates the master clutch and moves the shift lever. This requires both skill and experience.
Semi-automatic shift control enables automatic shifting between higher sequentially related forward gear ratios. A controller causes the engine fuel supply to be increased and decreased, possibly repeatedly, while actuators urge the existing engaged jaw clutch assembly toward disengagement to create a torque break sufficient for disengagement. However, engine acceleration and deceleration rates with some engines are significantly fast enough to cause jaw clutches to sometimes remain locked during electronically controlled torque reversals that facilitate disengagement. Some known fuel control systems xe2x80x9cblipxe2x80x9d torque positive and xe2x80x9cnegativexe2x80x9d in percentage increments and then hold the same for a given duration of time, in the manner similar to a step function, and then may increase as necessary to achieve disengagement. Negative torque may be induced by commanding zero fuel to the engine, allowing natural engine friction to provide the xe2x80x9cnegativexe2x80x9d torque reversal to the system.
A challenge that designers of semi-automatic transmission systems face is to improve or simplify the task of shifting gears and to do so in an efficient and effective manner that appears seamless to the driver. This invention provides an effective system and method for improving gear disengagement and shifting.
The present invention recognizes the aforementioned challenges and the limitations associated with conventional systems and methods and provides a torque modulation shift control system and method that improves gear disengagement in a cost-effective and efficient manner that appears seamless to the driver.
The present invention provides the additional advantage of being achievable with software modification. Hence, the system and method is quite economical when compared with conventional systems and methods.
In accordance with an embodiment of the invention, a shift control system is provided that is suitable for semi-automatic transmissions in heavy duty vehicles. The torque modulation system includes logic circuitry that may employ a torque function or algorithm to control the rate of change of torque, both positive and negative, and may provide for longer dwell time in the torque clutch disengagement range. Further, the dithering torque that is commanded by the system can, by way of example and without limitation, reduce momentary peak torque values from xc2x114% to xc2x110%, or less, using J1939 torque values over a datalink. The purpose of such dithering torque is to help ensure that xe2x80x9czero torquexe2x80x9d will be achieved in a relatively brief span of time even if the engine torque information is over or underreported to the system. Moreover, dwell time at maximum or minimum peak torque, which provides little or no functional benefit to disengagement and shifting, is not required. A method for improving gear disengagement and shift control in accordance with the principles of the invention is also disclosed.